It's worked nicely for two years, but this morning the tiles all load as pink, with errors like "400: Requested horizontal resolution: 0.0439453125 , best match: 0.03333333333333333 exceeds 10% threshold. Perhaps the client is configured with an incorrect set of scales (resolutions), or the DPI setting is off compared to the one in GWC?" if you view the image directly.

I'm pretty sure it does support EPSG:4326 - the problem seems to be something involving the resolutions available. However, I was unable to make EPSG:4326 work reliably, and switching to EPSG:900913 (the spherical mercator projection) at least got the maps working reliably. It also required a fair amount of rewriting since spherical mercator doesn't use lat/lon coordinates for points. See: docs.openlayers.org/library/spherical_mercator.html (Spherical Mercator OpenLayers docs). Accepting the answer since it solved my problem.
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Will MartinOct 5 '12 at 15:13